Bioskills Literature Review - Plant Pathology: Ralstonia Solanacerearum

BIOL 213

Bioskills Literature Review

Plant Pathology: Ralstonia Solanacerearum

Abstract

        There is a wide variety of plant pathogens that affect the world crops, but very few have as broad a range than Ralstonia Solanacerearum. It affects nearly 200 different species of plants, making the pathogen with one of the most diverse host groups. Most bacteria that affect plants are unable to cause much damage to the plant itself, but R. Solanacerearum is an exception. Destroying large areas of crops, it is one of the most economically damaging pathogens. Because of this destructive power, it is also one of the most important and frequently studied plant pathogens.  

Background

        R. Solanacerearum is a plant pathogen that is widely responsible for the disease known as bacterial wilt. It also goes by the names Moko disease in the bananas it affects, or Granville Wilt, named after a county in North Carolina, one of the first areas it was properly documented. It is mainly found in southern areas with healthy amounts of rain fall, as it flourishes in yearly temperatures over around 72 degrees. The name of the bacteria has had multiple iterations, the first being Bacillus solanacearum, then moving onto Pseudomonas solanacearum using this title for many years, then finally leading to the name used in this essay. There are four geographically distinct variations of R. Solanacerearum, the particular ones in Asia, America, Africa, and Oceania are labeled I-IV respectively.

Infection

        The pathogen is dispersed by many methods, one of which is the bacterial ooze byproduct. A sign of the infection, once a plant becomes a host it will seep a sticky ooze from the tissue. This ooze can drop into the soil and spread the bacteria through the soil. This process can lead to the infection being spread across wide areas of farm land. It can also spread by shedding of the roots of the infected plants, through tainted water via an irrigation system, or tools that contain the bacteria on them. Heather Olson, of NC State University says in her article Ralstonia Solanacerearum, that “the majority of hosts are dicots with the major exception being bananas and plantains.” There are also different races of the pathogen that affect specific groups of plants and the areas of which these hosts are found, such as race 1 which is found mostly in North and South America and is known to appear commonly in bananas. R. Solanacerearum is reported to have impressive survival skills. Although the population is decreased, it was revealed to have the capability to overwinter, meaning that it processes the ability to survive winters by lying dormant in plant debris or other “wild hosts.” This ability to overwinter means that farm land that is once affected by R. Solanacerearum must be given time to also recover, leaving it near unusable for several years.  

Symptoms

Since R. Solanacerearum is an agent from which bacterial wilt is transferred, the plants that are affected by the bacteria will visibly start to wilt. According to the Encyclopedia of Life, geraniums, one of the plants commonly affected by this pathogen, the “Wilting begins with lower leaves and petioles and works its way up the plant,” and eventually leads to the whole collapse of the plant. Since the pathogens most favorable working conditions are very warm days, it has potential to cease functioning during the evening and for tubers such as potatoes though, this is a period of time where the plants will fight back and at the end of the day the wilting from the bacteria will stop leaving the plant a recovery time during the night. Even though there is this period of healing, the plant will eventually cease being able to come back from the damage and ultimately die. The Penn State Extension, in their article Bacterial Wilt - Ralstonia solanacearum, says that internally “symptoms include light tan to yellow-brown discoloration of the vascular tissue. Long sections of infected stems reveals dark brown to black streaking in the vascular tissue as the disease progresses.” The xylem is the tissue that is mainly damaged from this bacterium.

Treatment

        R. Solanacerearum has proven resistant to any commercial chemical that has been used against it, as thus it is not a recommended means of trying to rid farm land of the disease. Because of this, strict sanitation practices must be put into place in areas where this bacterium is endemic. Bacteria free soil and plant materials must originally be used for growing and propagating, to avoid any future problems. If there are any noticeably infected plants or soil, it is to be discarded or removed from the overall population immediately, to ensure that there is no spread into the other organisms. Gaining tested and pathogen free stock plants and then establishing a system of preventing the bacterium from coming into contact with the stock plants. For greenhouse conditions, it is also crucial that the plants from the same source are kept together and separate from plants from other sources, as the health status of the plants introduced to the population is not entirely known and could potentially harm the already existing population. Keeping plants from the same source together allows for observation to be made of plants from different sources, so if there is any sign of contamination, the plants can be quickly removed.